Mercaptobenzothiazoles



2,695,299 Patented Nov. 23, 1954 fiice MERCAPTOBENZOTHIAZOLES JoachimDazzi, Dayton, Ohio, assignor to Monsanto Chemical Company, St. Louis,Mo., a corporation of Delaware No Drawing. Application June 23, 1950,Serial No. 170,049

3 Claims. (Cl. 260306) The present invention relates to new derivativesof 2- mercaptobenzothiazole and to methods of preparing the same.

The invention provides products having the general formula in which n isan integer of from I to 30 and R is a memberof the group consisting ofhydrogen and saturated hydrocarbon residues of from 1 to 29 carbonatoms.

One class of compounds having the above general formula includes membershaving the general structure in which R is a member of the groupconsisting of hydrogen and saturated hydrocarbon residues of from 1 to29 carbon atoms. This class of compounds includes esters of saturated,hydrocarbon monocarboxylic acids of from 1 to 30 carbon atoms and2(2-benzothiazylrnercapto)- ethanol. The latter compound is readilyobtainable by reaction of one mole of Z-mercaptobenzothiazole with onemole of ethylene oxide, ethylene glycol or ethylene chlorohydrin.

Another class of compounds includes esters of the saturated, hydrocarbonmonocarboxylic acids and products obtainable by reaction of one mole ofmercaptobenzothiazole with more than one mole of ethylene oxide. Thisclass has the general formula in which n is an integer of from 1 to 29and R is as herein defined. Condensation products of one mole of 2-mercaptobenzothiazole with from 5 to 30 moles of ethylene oxide aredescribed in the Gluesenkamp U. S. Patent No. 2,498,617, which isassigned to the same assignee as is the present case.

Accordingly, the present invention relates generally to esters ofsaturated, hydrocarbon monocarboxylic compounds of from 1 to 30 carbonatoms and a member of the group consisting of2-(Z-benzothiozylmercapto)ethanol and polyglycols obtained by reactingmercaptobenzothiazole with more than one mole of ethylene oxide, suchesters being obtained substantially according to the scheme in which isan integer of from 1 to 30, R is a hydrocarbon residue of from 1 to 29carbon atoms and X is a member of the group consisting of hydroxy, OCOR,chlorine and bromine. As carboxylic components there may be employed,for example, such aliphatic carboxy compounds as formic acid, acetylbromide, acetic anhydride, propionyl chloride, butyric anhydride,valeric acid, 2-ethylhexoic acid, lauroyl chloride, myristoyl bromide,behenic acid, cerotic acid and melissic acid; such aromatic compounds asbenzoyl chloride, 3-biphenyl carboxylic acid and Z-naphtoic acid; suchalicyclic compounds as cyclohexanecarboxylic acid andZ-methylcyclohexanecarboxylic acid; and such aralkyl compounds as 2-toluic acid, u-toluic acid, and hydrocinnamic acid.

Esterification of benzothiazylmercaptoethanol or of the higher ratiomercaptobenzothiazole-ethylene oxide condensation products with theabove carboxylic compounds takes place readily at ordinary, increased ordecreased temperatures depending upon the nature of the reactants. Whenusing the free acids, some esterification occurs upon contacting the tworeactants at ordinary temperatures, but optimum yields of the presentesters are obtained by heating a mixture of the mercapto compound andthe acid, preferably at refluxing .temperature and in the presence of anesterifying catalyst. As esterifying catalysts suitable for the presentpurpose may be mentioned acidic or basic materials such as sulfuricacid, phosphoric acid, p-toluenesulfonic acid, sodium methoxide, etc.

When working with acid halides optimum yields areobtained when operatingat decreased temperatures, i. e., at temperatures of, say, from minus 10C. to 10 C. With these highly reactive esterifying agents, the use of acatalyst is unnecessary and often detrimental to smooth condensation.

Inasmuch as the esterification reaction involves the con-, densation ofone mole of the hydroxy thiazole compound with one mole of the acid,stoichiometric proportions of the reactants are advantageously employed.However, since any excess of either the hydroxy compound or the acid maybe readily recovered from the final product, the quantity of reactantsemployed in the initial reaction is immaterial. It is preferred,however, to use an excess of the acid compound in order to minimizeincomplete esterification.

The present products are stable, somewhat high-boiling materials whichrange from viscous liquids to waxy or crystalline solids. They may beemployed for a variety of technical uses, i. e., as plasticizers forsynthetic resins and plastics, and as intermediates in the production ofmoisture-proofing agents, biological toxicants, surfaceactive agents,etc.

Advantageously employed as plasticizers, particularly for vinyl chloridepolymers, i. e., polyvinyl chloride and copolymers of vinyl chloridewith unsaturated monomers, are esters having the general structure moremay be mentioned the 2-(benzothiazylmercapto)- ethyl esters of valericacid, n-hexoic acid, pelargonic acid, laurie acid, 2-napthioic acid,hydrocinnamic acid and cyclohexanecarboxylic acid and the esters ofthese acids with Z-mercaptobenzothiazole-ethylene oxide condensationproducts in which the molar ratio of mercapto compound to ethylene oxideis 1:2 and 1:3.

I have found that esters of 2-(benzothiazylmercapto)- ethanol of ofZ-mercaptobenzothiazole-ethylene oxide condensation products having theformula shown above are of outstanding value as plasticizers forpolyvinyl chloride and for copolymers of at least per cent by weight ofvinyl chloride and up to 30 per cent by weight of an unsaturated monomercopolymerized therewith, for example vinyl acetate, vinylidene chloride,etc. These esters not only soften vinyl chloride polymers but alsoimpart a high degree of low temperature flexibility, very goodtemperature stability and great mechanical strength to these polymers.They are compatible with vinyl chloride polymers and show no exudationof plasticizer even at plasticizer content of up to 50 per cent.Although the quantity of plasticizer will depend upon the particularpolymer to be plasticized and upon its molecular weight, it is generallyfound that compositions having from per cent to 50 per cent by weight ofplasticizer will, in most cases, be satisfactory for general utility.The good flexibility of the plasticized compositions increases withincreasing plasticizer concentration.

In evaluating plasticizer efficiency use is made of the followingempirical testing procedures:

Compatibility.--Visual inspection of the plasticized composition isemployed, incompatibility of the plasticizer with the polymer beingdemonstrated by cloudiness and exudation of the plasticizer.

Low temperature flexibility.-Low temperature flexibility is one of themost important properties of elastomeric vinyl compositions. While manyplasticizers will produce flexible compositions at room temperature theflexibility of these compositions at low temperatures may varyconsiderably, i. e., plasticized polyvinyl chloride compositions thatare flexible at room temperature often become very brittle and uselessat low temperatures. Low temperature flexibility tests herein employedare according to the Clash-Berg method. This method determines thetorsional flexibility of a plastic at various temperatures. Thetemperature at which the vinyl composition exhibits an arbitrarilyestablished minimum flexibility is defined as the Low TemperatureFlexibility of the composition. This value may also be defined as thelower temperature limit of the plasticized compositions usefulness as onelastomer.

Water resistance.The amount of leaching that takes place when theplasticized composition is immersed in distilled water for 24 hours isdetermined.

The invention is further illustrated, but not limited, by the followingexamples:

Example I To a solution of 211.4 g. (1 mole) of2-(2-benzothiazylmercapto)ethanol (prepared by the reaction ofmercaptobenzothiazole with ethylene chlorohydrin) in an excess oftoulene there Was added 173 g. (1.2 moles) of 2-ethylhexoic acid and 5g. of p-toluenesulfonic acid as a catalyst. The resulting mixture wasthen refluxed for a time of 8 hours, during which time water was removedfrom the reaction zone as it was formed. Removal of the solvent andexcess 2-ethylhexoic acid from the resulting reaction product gavesubstantially pure 2-(2-benzothiazylmercapto)ethyl 2-ethylhexoate, B. P.201 C. to 208 C./0.7 mm. of mercury.

Example 2 To a solution of 110.6 g. (0.5 mole) of2-(2-benzothiazylmercapto)ethanol (prepared by reaction of henzothiazolewith ethylene oxide in 245.4 g. of xylene) there was added 33.9 g. ofdry pyridine and 50 ml. of ether. The resulting mixture was then cooledto a temperature of minus 5 C. to 0 C. and during a period of 42 minutesthere was added to the cooled mixture 85.5 g. (0.525 mole) of2-ethylhexoyl chloride. The whole was then stirred for 3.5 hours at atemperature of from minus 2 C. to 3 C., diluted with water, and washedneutral. Removal of the solvents by distillation at up to 100 C./l mm.pressure yielded 128 g. of crude 2-(2-benzothiazylmercapto)ethyl 2ethylhexoate, n =1.5608. Since the crude product was found to have anacid value of 9.67 percent (indicating the presence of unreacted acid)it was again submitted to esterification by refluxing it for a period of3 hours with 0.5 mole of 2-ethylhexoic acid in the presence of a smallamount of p-toluenesulfonic acid as esterifying catalyst and an excessof toluene as diluent. During this time 1.5 ml. of water was collected,showing further esterification. At the end of that time the product wasfractionally distilled to yield the substantially pure2-(Z-benzothiazylmercapto)ethyl 2-ethylhexoate, B. P. 200 C. to 210 C.at 0.7 mm., n =1.5625.

Example 3 Into a 250 ml. three-necked flask fitted with an agitator,thermometer and dropping funnel was placed 90 g. (0.1 mole) of a 23.5percent solution of 2-(2-benzothiazylmercapto)ethanol in p-xylene and 9g. (0.11 mole) of pyridine. The mixture was cooled in a saltice bathwhile 24.7 g. (0.1 mole) of myristoyl chloride was added over a periodof one hour. The flask contents were stirred an additional hour while inthe ice bath and then for another 80 minutes at room temperature. Thereaction mixture was washed two times with water, once with a dilutesodium bicarbonate solution, three more times with water, dried overcalcium chloride, filtered and distilled under reduced pressure to a pottemperature of 80 C./ 3 mm. There was thus obtained 39 g. of2-(2-benzothiazylmercapto)ethyl myristate as residue.

Proceeding substantially as in the above examples 2-(2-benzothiazylmercapto)ethanol may be similarly reacted with othersaturated, unsubstituted monocarboxylic acids of from 1 to 30 carbonatoms. Thus, instead of the carboxylic acids employed in the aboveexamples there may be used, e. g., acetic acid, butyric acid, n-caproicacid, capric acid, stearic acid, cyclohexanecarboxylic acid, a-toluicacid, benzoic acid, 4-phenylbenzoic acid, etc. to yield the2-(Z-benzothiazylmercapto)ethyl esters thereof. Also, instead of2-(Z-benzothiazylmercapto)ethanol there may be employed reactionproducts of one mole of 2- mercaptobenzothiazole with more than one moleof ethylene oxide, i. e., condensation products prepared from one moleof Z-mercaptobenzothiazole and from 2 to 30 moles of ethylene oxide.

Example 4 Sixty parts of polyvinyl chloride and 40 parts by weight ofthe 2-(2-benzothiazylmercapto)ethyl 2-ethylhexoate, B. P. 200 to 210 C.of Example 2 are mixed on a rolling mill to a homogeneous blend. Duringthe milling there was observed substantially no fuming anddiscoloration. A molded sheet of the mixture was clear and transparentand substantially colorless. Testing of the molded sheet for lowtemperature flexibility, according to the testing procedure describedabove, gave a value of minus 26 C., which value denotes extremely goodlow temperature properties. Tests of the water-resistance properties ofthe plasticized material employing the test procedure described aboveshowed a solids-loss of only 0.2 percent.

Instead of the 2 (2 benzothiazylmercapto)ethyl 2 ethylhexoate employedin the above example there may be advantageously employed asplasticizers for polyvinyl chloride and for copolymers of vinyl chlorideother esters having the general structure in which n is an integer offrom 1 to 3 and R is a member of the group consisting of alkyl, aryl,aralkyl and cycloalkyl radicals of from 4 to 12 carbon atoms, e. g., the2-(benzothiazylmercapto)ethyl esters of butyric acid, capric acid,lauric acid, 4-toluic acid, hydrocinnamic acid or cyclohexanecarboxylicacid. Also, instead of using the 2-(benzothiazylmercapto)ethyl esters ofthese acids there may be employed esters of the above acids and thecondensation products of one mole of 2-mercaptobenzothiazole with from 2to 3 moles of ethylene oxide.

While the above example particularly illustrates compositions in whichthe ratio of plasticizer to polymer content is 40:60, this ratio beingemployed in order to get comparable efliciencies, the content of esterto polyvinyl chloride may be widely varied, depending upon theproperties desired in the final product. For many purposes a plasticizercontent of, say, from only 10 percent to 20 percent is preferred. Theabove esters are compatible with polyvinyl chloride over wide ranges ofconcentrations, up to 50 percent of esters based on the total weight ofthepla'sticized composition yielding desirable products.

Although the invention has been described particularly with reference tothe useof the present esters as plasticizers for polyvinyl chloride,these esters are advantageously employed also as plasticizers forcopolymers of vinyl chloride, for example the copolymers of vinylchloride with vinyl acetate or'vinylidene chloride, etc.

Preferably such copolymers have a high vinyl chloridecontent, i. e., avinyl chloride content of at least 70 per- 6 cent by weight of vinylchloride and up to 30 percent by in which n is an integer of from 1 to 3and R is an alkyl Weight of the copolymerizable monomer. radical of from4 to 14 carbon atoms.

The plasticized polyvinyl halide compositions of the 2.2-(2-benzothiazylmercapto)ethyl 2-ethy1hexoate. present invention havegood thermal stability; however, 3. 2-(Z-benzothiazylmercapto)ethylmyristate. for many purposes it may be advantageous to use known 5stabilizers in the plasticized compositions. The esters References Cited111 the file 0f thlS Patent are of general utility in softening vinylchloride polymers. UNITED STATES PATENTS They may be used as the onlyplasticizing component in a compounded vinyl chloride polymer or theymay be Number Name Date used in conjunction with other plasticizers. 1075,0 le a der 00L 3, 1939 WhatIclaimis: 2,175,049 Alexander Oct. 3,1939 1. Compounds having the general formula 1 l f r A g- 1 1 402,280,792 Bruson Apr. 28, 1942 2,323,037 Harman June 29, 1943 g 152,407,138 Clifford et a1 Sept. 3, 1946 S(CHzOHaO),,OGR 2,498,617Gluesenkamp Feb. 21, 1950

1. COMPOUNDS HAVING THE GENERAL FORMULA